High-fat diets linked to some types of breast cancer

NEW YORK (Reuters Health) - Women who eat a lot of fat,
particularly saturated fat, may be at higher risk of certain
types of breast cancer, new research suggests.

Past studies have come to differing conclusions on a
possible association between dietary fat and breast cancer.
Whether the two are even linked at all remains controversial.

The new report, a second analysis of a large, long-term
study, suggests that fat may play a role in the development of
certain forms of the disease but not others, the authors said.

Still, it cannot prove that a high-fat diet is the reason
any of the women got cancer.

"In our study we confirm that saturated fat intake was
positively associated with breast cancer risk," lead author
Sabina Sieri, from the Fondazione IRCCS National Cancer
Institute in Milan, Italy, told Reuters Health in an email.

"Saturated fatty acids intake should be as low as possible
within the context of a nutritionally adequate diet."

Saturated fat in the diet most often comes from meat and
other animal products like butter and cheese.

The research team's findings are based on a study of about
337,000 women from 10 European countries. They filled out
questionnaires about their diet and lifestyle and were followed
for an average of 11 to 12 years.

During that time, about 10,000 of the women were diagnosed
with breast cancer.

The original study found that women who ate the most
saturated fat were more likely to develop breast cancer than
those who ate the least.

For the new analysis, the researchers used patient medical
records to classify breast cancers into specific subtypes, for
instance based on whether the tumor may respond to the hormones
estrogen and progesterone.

They found that women with diets high in saturated fat were
28 percent more likely to develop tumors that had receptors for
estrogen and progesterone than women with the lowest saturated
fat in their diets. The pattern was similar for total fat
intake.

However, the chance of developing breast tumors without
receptors for those hormones was not linked to dietary fat,
according to the findings published in the Journal of the
National Cancer Institute.

The researchers said it's possible dietary fat increases the
level of sex hormones in the body. That could explain why
high-fat diets are tied to a greater risk of tumors whose growth
is related to estrogen and progesterone, known as
hormone-receptor-positive cancers. Those cancers make up the
majority of breast cancer diagnoses.

Sieri and colleagues found that high levels of saturated fat
were also linked to a greater risk of HER2 negative breast
cancer, but not HER2 positive disease. HER2 stands for human
epidermal growth factor receptor 2 and is one factor used to
determine how fast a cancer is growing.

What's more, he added, "These patients were not randomly
assigned to follow one diet or another."

That means other differences between women who ate high- and
low-fat diets may have factored into their cancer risk.

Still, Hudis said, the findings are consistent with recent
research looking at specific types of breast cancer and make
sense based on what is known about the biological effects of
dietary fat.

Dr. Michelle Holmes, who has studied diet and breast cancer
at Harvard Medical School and the Harvard School of Public
Health in Boston, said that in the grand scheme of things, any
possible link between fat and breast cancer still seems to be
small.

"In my opinion, the bottom line is that if the association
with fat and breast cancer exists, it's fairly small (and) it's
probably limited to certain subtypes," Holmes told Reuters
Health.

Even though the new study included a "huge" number of women,
she said, "the answer doesn't leap out at you."

Hudis and Holmes, who were not involved in the new research,
agreed there's no reason women shouldn't still cut back on
saturated fat.

"Saturated fat is bad for heart disease anyway," Holmes
said.

"The associations with dietary fat are much stronger for
heart disease, which still kills more women than breast cancer
in the United States."

SOURCE: http://bit.ly/1rjQum8 Journal of the National Cancer
Institute, online April 9, 2014.